Estudo do Desempenho Lubri-refrigerante de Fluidos de Corte Submetidos a Biodegradação Microbiológica

Abstract

Almost all stages of metal transformation involve the use of a cutting fluids (CFs), making them ubiquitous in all types of industries dedicated to cutting of metals. They influence heat generation in the machining processes by reducing friction between the tool and the chip / workpiece and provide cooling by dissipating the heat generated by both conduction and convection. Their lubri-cooling properties contribute to the prevention of thermal damage to the workpiece material and reduce the wear of the cutting tool, improving the process performance. In addition, they provide protection to the system in which they circulate, to the workpiece and to the tool against oxidation / corrosion. However, in spite of the many benefits, when contaminated by microorganisms, they cause harm to human, the environment and the industry itself, which loses money caused by the reduction of its technical efficiency in production, early disposal, treatment of toxic waste and days off due to illness of machine operators. In this study, the performance of two cutting fluids (an emulsion of vegetal base and a semi-synthetic of mineral base), in four concentrations (3, 5, 8 and 10%) were tested to determine the compromise of physical-chemical, lubricant, coolant and anticorrosive properties after seven and seventy days of microbiological contamination, totaling 24 fluid samples. Physical-chemical tests (pH, dynamic and kinematic viscosities, specific mass, thermal conductivity, thermal diffusivity, specific heat and contact angle with a metal surface - wettability test) were carried out to characterize the intrinsic properties of the fluids. The lubricant and coolant performances were determined in tribological tests (pendular sclerometry and reciprocating) as well as in machining tests (drilling and turning processes). Specific tests were also carried out to determine the cooling ability and the corrosion properties. The results showed three possibilities for these two cutting fluids when contaminated by microorganisms for seven and seventy days: in some concentrations the microbiological contamination worsened the physico-chemical, lubrication and cooling properties of the CFs, improving them or remaining stable in other concentrations. In all the cases these effects were quantified and analyzed. However, a reduction of the anticorrosive property was verified for the two CFs, being more intense after microbiological contamination by seventy days, with greater aggravation for the mineral base. This study was able to determine the harmful effect of the microbiological contamination for the machining process, even though in some parameters this contamination improved the results. Thus, considering its unavoidable presence in the cutting fluids, further studies are necessary to better determine the microbial load / species / nutrients / competition and symbiosis / technological innovation / biocompatibility / performance ( fluid and microorganism) / type of waste generated when discarding / treating this waste, among other parameters. All of them isolated and together must be harmonically aligned, so that they can favor both the machining process and production as a whole, as well as the desired properties of the fluid, thus ensuring the necessary safety to the sustainability tripod that supports it (industry / operator / Environment), in their manufacture, application, manipulation, monitoring and disposal.